Ambulatory phrenic nerve stimulation detection

ABSTRACT

An example of a system includes an implantable medical device (IMD) for implantation in a patient, where the IMD includes a cardiac pace generator, phrenic nerve stimulation (PS) sensor, a memory, and a controller, and where the controller is operably connected to the cardiac pace generator to generate cardiac paces. The controller is configured to provide a trigger for conducting a PS detection procedure and perform the PS detection procedure in response to the trigger. In performing the PS detection procedure the controller is configured to receive a signal from the sensor, detect PS using the signal from the sensor, and record the PS detection in storage within the IMD.

CLAIM OF PRIORITY

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Patent Application Ser. No. 61/779,772, filed onMar. 13, 2013, which is herein incorporated by reference in itsentirety.

TECHNICAL FIELD

This application is related generally to medical devices and, moreparticularly, to systems, devices and methods that detect pace-inducedphrenic nerve stimulation.

BACKGROUND

Implanted pacing systems may be used to pace the heart. When the heartis paced in the left ventricle (LV), for example, there may be unwantedstimulation of the phrenic nerve that causes contraction of thediaphragm. Unintended phrenic nerve activation (an unintended actionpotential propagated in the phrenic nerve that causes a noticeablediaphragm contraction) is a well-known consequence of left ventricularpacing. The left phrenic nerve, for example, descends on the pericardiumto penetrate the left part of the diaphragm. In most people, the leftphrenic nerve runs close to the coronary vein targets for LV leadplacement. The unintended phrenic nerve activation may cause thediaphragm to undesirably contract. Unintended phrenic nerve activationmay feel like hiccups to the patient. Such unintended phrenic nerveactivation can occur when the electric field of the LV pacing lead isproximate to the left phrenic nerve and is at a stimulation output thatis strong enough to capture the nerve. Unintended phrenic nerveactivation may vary from patient to patient. One reason for thisvariance is that the anatomic location of the phrenic nerve can varywithin patients. Additionally, the veins in which the cardiac lead maybe placed are not always in the same location with respect to theventricle and the nearby passing nerve. Also, the selected position inwhich to place a cardiac lead for a prescribed cardiac therapy may vary.

Although phrenic nerve stimulation is commonly assessed at implant,unintended phrenic nerve activation caused by phrenic nerve captureduring pacing may first appear or worsen post-implant for a variety ofreasons. Therefore, special office visits after implant may be necessaryor desirable to reprogram the device or worse, surgically reposition thelead to avoid phrenic nerve stimulation.

SUMMARY

An example of a system includes an implantable medical device (IMD) forimplantation in a patient. The IMD may include a cardiac pace generator,a phrenic nerve stimulation (PS) sensor, a memory, and a controller. Thecontroller may be operably connected to the cardiac pace generator togenerate cardiac paces. The controller may be configured to provide atrigger for conducting a PS detection procedure and perform the PSdetection procedure in response to the trigger. In performing the PSdetection procedure the controller may be configured to receive a signalfrom the PS sensor, detect PS using the signal from the PS sensor, andrecord the PS detection in storage within the IMD.

An example of a system comprises an implantable medical device (IMD) forimplantation in a patient. The IMD may include a cardiac pace generator,phrenic nerve stimulation (PS) sensor, a memory, and a controller. Thecontroller may be operably connected to the cardiac pace generator togenerate cardiac paces, and the controller may include a trigger module,a recognition module, a PS test module and a decision module. Thetrigger module may be configured to provide a trigger for a PS detectionprocedure and to perform the base test. In performing the base test thetrigger module may be configured to: detect an amplitude of the signalfrom the PS sensor, compare the sensed amplitude to a threshold todetect PS, and provide the trigger from the trigger module when thesensed amplitude is higher than the threshold. The recognition modulemay be configured to analyze a signal from the PS sensor to confirm thePS detection from the base test. The PS test module may be configured torespond to the PS detection confirmed by the recognition module. Inresponding to the PS detection confirmed by the recognition module, thePS test module is configured to further analyze the signal from the PSsensor to provide further confirmation of the PS detection. Confirmationby the PS test module may provide greater confidence than confirmationby the recognition module. The decision module may be configured torecord the PS detection in the storage within the IMD, automaticallychange a current pacing configuration to another pacing configurationbased at least in part on PS detection, or communicate an alert to anexternal device based at least in part on PS detection.

An example of a method is performed using an implantable medical device(IMD) within an ambulatory patient, where the IMD includes anaccelerometer sensor for phrenic nerve stimulation (PS) detection. Themethod may comprise triggering a PS detection procedure using the IMDwithin an ambulatory patient, and performing the PS procedure inresponse to the trigger, wherein performing the PS procedure includesproviding a signal from the PS detector, detecting PS using the signalfrom the PS detector, and recording the PS detection in storage withinthe IMD.

This Summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details about thepresent subject matter are found in the detailed description andappended claims. The scope of the present invention is defined by theappended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are illustrated by way of example in the figures ofthe accompanying drawings. Such embodiments are demonstrative and notintended to be exhaustive or exclusive embodiments of the presentsubject matter.

FIG. 1 illustrates, by way of example, an embodiment of an implantablemedical device (IMD) configured to deliver myocardial stimulation.

FIG. 2 illustrates, by way of example, an embodiment of an IMD.

FIG. 3 illustrates, by way of example, an embodiment of a system thatincludes two or more IMDs.

FIG. 4 illustrates, by way of example, an embodiment of a system thatincludes the IMD, such as a cardiac rhythm management device, anexternal device such as a programmer, and an external PS sensor.

FIG. 5 illustrates, by way of example, a system diagram of an embodimentof a microprocessor-based implantable device.

FIGS. 6A-6E illustrate, by way of example, various embodiments of asystem for performing a PS detection procedure.

FIG. 7 illustrates an example of using a threshold 604 for an amplitudeof signal from a PS sensor to trigger a PS detection routine.

FIGS. 8A-8B illustrate an example of streaming signal from anaccelerometer XL, where FIG. 8A illustrates no PS in the streamingsignal and FIG. 8B illustrates occurrences of PS in the streamingsignal.

FIGS. 9A-9B illustrate schematic diagrams for an example of performing aPS test across two potential pacing configurations and storing theresults of the test.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refersto the accompanying drawings which show, by way of illustration,specific aspects and embodiments in which the present subject matter maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the present subject matter.Other embodiments may be utilized and structural, logical, andelectrical changes may be made without departing from the scope of thepresent subject matter.

References to “an,” “one,” or “various” embodiments in this disclosureare not necessarily to the same embodiment, and such referencescontemplate more than one embodiment. The following detailed descriptionis, therefore, not to be taken in a limiting sense, and the scope isdefined only by the appended claims, along with the full scope of legalequivalents to which such claims are entitled.

Some embodiments, for example, implement an automatic detectionalgorithm for detecting unintended phrenic nerve activation (alsoreferred to herein as pace-induced phrenic nerve stimulation or asphrenic nerve stimulation “PS”). According to various embodiments, thePS detection procedure can be used in a clinical setting such as duringimplant procedures or in patient follow-up visits, or in an ambulatorysetting such as in a patient's home, or in both the clinical andambulatory setting. The PS detection procedure can lessen or alleviatethe burden of the patients and clinical staff to adequately address theproblems of unintended PS that can occur during myocardial stimulation.For example, the ability to accurately and/or automatically detect PScan reduce prolonged discomfort for patients experiencing PS, and canreduce the burden on hospitals and staff for testing and reprogrammingdevices.

As PS may be an unintended side effect of some cardiac pacing therapies,a brief discussion of myocardial stimulation and the phrenic nerve isprovided below.

Myocardial Stimulation and the Phrenic Nerve

A myocardial stimulation therapy may deliver a cardiac therapy usingelectrical stimulation of the myocardium. Some examples of myocardialstimulation therapies, and devices for performing the therapies, areprovided below. A pacemaker is a device which paces the heart with timedpacing pulses, most commonly for the treatment of bradycardia where theventricular rate is too slow. If functioning properly, the pacemakermakes up for the heart's inability to pace itself at an appropriaterhythm in order to meet metabolic demand by enforcing a minimum heartrate. Implantable devices have also been developed that affect themanner and degree to which the heart chambers contract during a cardiaccycle in order to promote the efficient pumping of blood. The heartpumps more effectively when the chambers contract in a coordinatedmanner, a result normally provided by the specialized conductionpathways in both the atria and the ventricles that enable the rapidconduction of excitation (i.e., depolarization) throughout themyocardium. These pathways conduct excitatory impulses from thesino-atrial node to the atrial myocardium, to the atrio-ventricularnode, and then to the ventricular myocardium to provide a coordinatedcontraction of both atria and both ventricles. This both synchronizesthe contractions of the muscle fibers of each chamber and synchronizesthe contraction of each atrium or ventricle with the contralateralatrium or ventricle. Without the synchronization afforded by thenormally functioning specialized conduction pathways, the heart'spumping efficiency is greatly diminished. Pathology of these conductionpathways and other inter-ventricular or intra-ventricular conductiondeficits can be a causative factor in heart failure. Heart failurerefers to a clinical syndrome in which an abnormality of cardiacfunction causes cardiac output to fall below a level adequate to meetthe metabolic demand of peripheral tissues. In order to treat theseproblems, implantable cardiac devices have been developed that provideappropriately timed electrical stimulation to one or more heart chambersin an attempt to improve the coordination of atrial and/or ventricularcontractions, termed cardiac resynchronization therapy (CRT).Ventricular resynchronization is useful in treating heart failurebecause, although not directly inotropic, resynchronization can resultin a more coordinated contraction of the ventricles with improvedpumping efficiency and increased cardiac output. A CRT example appliesstimulation pulses to both ventricles, either simultaneously orseparated by a specified biventricular offset interval, and after aspecified atrio-ventricular delay interval with respect to the detectionof an intrinsic atrial contraction or delivery of an atrial pace.

CRT can be beneficial in reducing the deleterious ventricular remodelingwhich can occur in post-myocardial infarction (MI) and heart failurepatients, which appears to occur as a result of changes in thedistribution of wall stress experienced by the ventricles during thecardiac pumping cycle when CRT is applied. The degree to which a heartmuscle fiber is stretched before it contracts is termed the preload, andthe maximum tension and velocity of shortening of a muscle fiberincreases with increasing preload. When a myocardial region contractslate relative to other regions, the contraction of those opposingregions stretches the later contracting region and increases thepreload. The degree of tension or stress on a heart muscle fiber as itcontracts is termed the afterload. Because pressure within theventricles rises rapidly from a diastolic to a systolic value as bloodis pumped out into the aorta and pulmonary arteries, the part of theventricle that first contracts due to an excitatory stimulation pulsedoes so against a lower afterload than does a part of the ventriclecontracting later. Thus a myocardial region which contracts later thanother regions is subjected to both an increased preload and afterload.This situation is created frequently by the ventricular conductiondelays associated with heart failure and ventricular dysfunction due toan MI. The increased wall stress to the late-activating myocardialregions may be the trigger for ventricular remodeling. Pacing one ormore sites may cause a more coordinated contraction, by providingpre-excitation of myocardial regions which would otherwise be activatedlater during systole and experience increased wall stress. Thepre-excitation of the remodeled region relative to other regions unloadsthe region from mechanical stress and allows reversal or prevention ofremodeling to occur.

Cardioversion, an electrical shock delivered to the heart synchronouslywith the QRS complex, and defibrillation, an electrical shock deliveredwithout synchronization to the QRS complex, can be used to terminatemost tachyarrhythmias. The electric shock terminates the tachyarrhythmiaby simultaneously depolarizing the myocardium and rendering itrefractory. A class of CRM devices known as an implantable cardioverterdefibrillator (ICD) provides this kind of therapy by delivering a shockpulse to the heart when the device detects tachyarrhythmias. Anothertype of electrical therapy for tachycardia is anti-tachycardia pacing(ATP). In ventricular ATP, the ventricles are competitively paced withone or more pacing pulses in an effort to interrupt the reentrantcircuit causing the tachycardia. Modern ICDs typically have ATPcapability, and deliver ATP therapy or a shock pulse when atachyarrhythmia is detected. ATP may be referred to as overdrive pacing.Other overdrive pacing therapies exist, such as intermittent pacingtherapy (IPT), which may also be referred to as a conditioning therapy.

Both a right phrenic nerve and a left phrenic nerve pass near the heartand innervate the diaphragm below the heart. Pace-induced phrenic nervestimulation, also referred to herein as PS, may be observed with variousforms of pacing. PS may be observed particularly with LV pacing becauseof the close proximity of the LV pacing site to the left phrenic nerve.PS is a common side effect of CRT. Cardiac stimulation at otherlocations of the heart may result in PS in either the left or rightphrenic nerve. The present subject matter is not limited to PS of theleft phrenic nerve during LV pacing, but may be implemented toappropriately address PS in either the left or right phrenic nervecaused by myocardial stimulation or other stimulation.

During a cardiac lead implant procedure such as an LV lead implant, forexample, a physician may test for the presence of phrenic nervestimulations (PS) for different pacing configurations and differentstimulation parameters. Examples of pacing configurations can include,but are not limited to, LV bipolar, LV to can, and LV to right ventricle(RV) and examples of stimulation parameters can include an amplitude(e.g. voltage) and pulse width of stimulation pulses. Accordingly, thephysician can program the IMD to deliver the cardiac therapy using onlythose pacing configurations or the stimulation parameters of the cardiactherapy that inhibits the unintended PS.

The PS procedure is capable of addressing problems with automaticallydetecting PS. Even when a patient is sitting quietly, it can bedifficult to sense signals close to the PS threshold as the signal canbe small. A PS threshold represents a smallest pacing parameter, such asa pacing amplitude for an LV pace, at which it can be determined that PSoccurs with the pace. Thus, for example, PS is determined to generallyoccur when the pacing amplitude is equal to or greater than the PSthreshold. PS may not occur for every pace equal to or greater than thePS threshold.

For example, it can be difficult to process low-peak-to-peak amplitudesof sensed PS responses from the deflection variations observed in theaccelerometer or other PS sensor, especially those close to the PSthreshold. It can also be difficult to detect PS because differentpatients have PS responses of various amplitudes and morphologies.

PS may be observed only when a patient is in a particular position (e.g.lying down) or when participating in certain activities or activitylevels. The PS may not have been observed at the time that thestimulation device was implanted because of the patient position at thetime of implantation, because of the effects of anesthesia, or becauseof other factors that are not present in a clinical setting.

FIG. 1 illustrates, by way of an example, an implantable medical device(IMD) 100 coupled to a patient's heart and configured to delivermyocardial stimulation for pacing therapy and/or sense cardiac events.The IMD 100 can be used to deliver a cardiac tissue stimulation therapy,such as a cardiac rhythm management therapy (CRT) or other pacingtherapies, using leads represented by the dotted lines and electrodesrepresented by “X” fed into the right atrium, right ventricle, andcoronary sinus of the heart. The lead 101 passing through the coronarysinus of the heart includes a left ventricular (LV) electrode 102, orelectrodes, for use to stimulate the left ventricle at a stimulationsite. In an example, the lead 101 can be a multipolar lead, including aplurality of electrodes and corresponding conductors. In an example, thelead 101 can include four discrete electrodes, such as: a tip electrode,a first ring electrode, a second ring electrode, and a third ringelectrode. In an example, the electrodes can be located near a distalportion of the lead 101. Similarly the IMD 100 can include a leadpositioned to stimulate the right ventricle (RV) and including aplurality of electrodes, such as a tip electrode and one or more ringelectrodes. The IMD 100 can itself be configured as a Can electrode byusing a conductive housing of the IMD 100. Electric potential developedbetween different electrodes can be used to provide a plurality ofpacing configurations of pacing vectors available in the IMD 100. Thepacing configurations involving LV electrodes use the LV electrode 102,which may be relatively close to a left phrenic nerve 103 of thepatient. PS may occur for certain configurations of pacing vectors orelectrode placement.

PS may also occur due to certain factors including but not limited tochanges in the patient's body position, LV lead micro-dislodgement,cardiac reverse remodeling, changes in a stimulation thresholdassociated with PS, referred to herein as a PS threshold, or any othersuch factor. For example, PS can occur due to dislodgement of an acutelyimplanted lead or a chronically implanted lead. PS can occur morefrequently in an acutely implanted lead as compared to a chronicallyimplanted lead due to relative instability of the acutely-implantedlead. As the acutely implanted lead remains implanted for a largerperiod of time, tissue growth can occur around the lead. This impartsrelative stability to the lead. Increased stability can then causechanges in the manner in which the lead affects PS. Thus, PS thresholdcan be unstable and vary with a number of factors. The instability of PScan be more frequent in an ambulatory setting rather than in a clinicalsetting. Detection of PS in the ambulatory setting can involve using aplurality of sensors. Various examples of the present subject matter canbe used in processes for using PS sensor(s) to detect PS. A PS sensorcan be used to detect phrenic nerve activity. By way of example and notlimitation, a PS sensor can detect motion caused by the diaphragminduced by PS. For example, some examples can use an accelerometer todetect PS. Other examples of sensors that can be used to detect PSinclude, but are not limited to, a posture sensor, an acoustic sensor, arespiration sensor, an impedance sensor, a neural sensor on the phrenicnerve, a metabolic sensor, or an electromyogram (EMG) sensor for sensingsignals indicative of diaphragm contraction. Some examples use a posturesensor to provide context. Some examples use an activity sensor toprovide context. Some examples use a timer to determine a time of day toprovide context. Some examples allow the device to store posture,activity, time of day and the like with the detected PS data todetermine the context when the PS is observed.

FIG. 2 illustrates an example of the implantable medical device (IMD)100. The IMD 100 includes a controller 202, a cardiac pace generator206, a PS sensor 206, a cardiac activity sensor 208, a memory 210 andother sensor(s) 212. In various examples, the one or more other sensors212 can include, by way of example and not limitation, a sensor used fordetecting posture, a sensor used for detecting respiration or arespiration cycle, a metabolic sensor, a pressure sensor, a temperaturesensor, a minute ventilation sensor, an impedance sensor, a muscle noisesensor, or a sensor used for detecting activity. The controller 202 caninclude one or more timer(s) 214, a PS threshold test module 216, apacing vector control module 218, and an ambulatory PS detector 220. Theambulatory PS detector 220 may include a trigger module 222, arecognition module 224, a PS test module 226, and a decision module 228.

In an example, the IMD 100 can implement a cardiac pacing algorithm, inwhich the controller 202 receives sensed cardiac activity from thecardiac activity sensor 208, uses timer(s) 214, such as a cardiac pacingtimer, to determine a pace time for delivering a cardiac pace or othermyocardial stimulation pulse, and controls the cardiac pace generator204 to deliver the cardiac pace at the desired time. The IMD 100 canstore data associated with the cardiac pacing algorithm, as well asother data, such as data from other sensors 212 or data associated withthe ambulatory PS detector 220 in the memory 210 of the IMD 100.

The PS threshold test module may be configured to determine PSthresholds for different available pacing configurations. The PSthreshold represents a boundary for pacing parameters separatingparameter(s) when PS may be observed and parameter(s) when PS is notexpected to be observed. The pacing configurations may be controlledusing the pacing vector control 218 module

The controller 202 can include the PS detector 220 which can beconfigured to detect PS during myocardial stimulation. As it forms partof IMD 100, the ambulatory PS detector 220 can be used to detect PS inambulatory patients. In some examples, the PS detector 220 includes thetrigger module and the decision module. In some examples, the PSdetector includes the trigger module, the recognition module and thedecision module. In some examples, the ambulatory PS detector includesthe trigger module 222, the recognition module 224, the PS test module226 and the decision module 228.

The trigger module 222 can be configured to monitor one or more sensorsto receive a trigger to conduct a PS procedure in response to thetrigger. The sensor(s) include the PS sensor, such as an accelerometer.However, the sensor(s) may also include other sensor(s) 212. The triggercan be defined based on an output of the sensor(s). For example, thetrigger module 222 can be configured to monitor the accelerometer of thePS sensor 206 to determine when a signal from the accelerometer crossesa predefined amplitude threshold that functions as a trigger threshold.In some example, a threshold may function as the trigger threshold. Thecrossing of the predefined amplitude threshold by the accelerometersignal during PS threshold test can then be defined as the trigger forconducting the PS procedure. However, the trigger threshold may be othertrigger(s) to be more inclusive of signals that may potentially includePS. At least one other trigger can be defined including, but not limitedto, a time duration expiration (such as trigger PS procedure every “X”hours, or “Y” days post implant), an LV Auto-Threshold (LVAT) test whichautomatically determines the threshold for capturing myocardia, a leaddislodgement event, a pacing parameter change, a detection of reverseremodeling, a user-initiation of the PS procedure, or feature(s) of thesensed signal other than or in addition to amplitude. In an example, acombination of triggers can be used as the trigger for conducting the PSprocedure.

The trigger received by the trigger module 222 may be adequate toidentify PS. However, some examples provide one or more additionalmodule(s) (recognition module 224 and/or PS test module 226) to furtheranalyze the sensed signal to ensure the accuracy of PS indication. Thatis, these additional module(s) may provide higher level(s) of confidencethat PS has occurred.

For example, the recognition module 224 can be configured to analyze thesignal to confirm the presence of PS. In a sense, the recognition module224 may function as an intermediate PS test by analyzing more of thesensed signal than the trigger module 222, and may function as a “gatekeeper” before a more robust PS test is conducted by a PS test module226. In an example, the recognition module 224 can be configured tostore information pertinent to the signal. For example, the recognitionmodule 224 can be configured to respond to the trigger from the triggermodule 222 and record the sensed signal for a certain amount of time.The stored signal may be a raw signal from the sensor or may be afiltered signal. In an example, the signal may be continually recordedin a circular buffer storage rather than only being recorded in responseto the trigger from the trigger module 222. Thus, for example, if thetrigger module 222 is configured to provide a trigger when an amplitudeof the sensed signal crosses a threshold, the recognition module canevaluate the stored signal to confirm that the stored signal isconsistent with PS. For example, the recognition module 224 may store Tseconds of the sensed signal for further analysis.

In an example, the recognition module 224 can be configured to have atleast some capabilities to change certain device sensing/pacingparameters. Some examples of active capabilities include but are notlimited to forcing a maximum output pacing limited by a ceiling in thecurrent pacing vector or forcing a minimum output pacing limited by afloor in the current vector. Some other examples of active capabilitiesinclude pacing in refractory of the heart, which ensures sensing of thePS response rather than a response to cardiac capture (such as heartsounds). Some embodiments may implement the recognition module inhardware, and some examples may implement the recognition module infirmware. The recognition module 224 may analyze PS beats to confirmthat the evaluated signal is consistent with PS if M of N PS beats areconfirmed as being consistent with PS. A PS beat is a PS signalassociated with a cardiac pace. If the recognition module 224 confirmsthat the evaluated signal is consistent with PS, then some embodimentsmay initiate a more robust test using the PS test module 226. Someembodiments will instead trigger the decision module 228 if therecognition module 224 confirms that the evaluated signal is consistentwith PS.

The PS test module may implement one or more of the PS detectionalgorithms disclosed in U.S. application Ser. No. 13/781,133 entitled“Baseline Determination For Phrenic Nerve Stimulation Detection” filedFeb. 28, 2013, U.S. application Ser. No. 13/781,042 entitled“Determination of Phrenic Nerve Stimulation Threshold” filed Feb. 28,2013, and U.S. application Ser. No. 13/781,177 entitled “Phrenic NerveStimulation Detection” filed Feb. 28, 2013, and U.S. App. No. 61/670,870entitled “Adapted Phrenic Nerve Stimulation Detection.” filed Jul. 12,2012.

By way of example, a relatively simple PS test may be implemented todetect for PS presence only in the current pacing vector, a moremoderate PS test may be implemented to detect for PS presence in auser-limited list of available pacing vectors, and a more complex PStest may be implemented to detect for PS presence in all availablepacing vectors. A pacing vector represents some combination of sourceand sink electrodes. An example of a user-limited list of availablepacing vectors is a list of vectors having a common or defaultanode/return electrode. Some embodiments may change the device settingsto search for PS. The results of these tests may provide the decisionmodule 228 with information for an ambulatory vector change and/bestored and presented at patient follow-up visits to simplify pacingreprogramming. The exhaustive threshold search in all vectors may workwith an auto-threshold algorithm, such as LV auto-threshold (LVAT)algorithms, for example, to recall or to newly determine pacingthresholds, allowing the identification of the next best pacing vector.

An outcome of the PS test module 226 can be used to decide whether thecurrent or any other pacing configuration causes the occurrence of thePS. Accordingly the IMD 100 can be reprogrammed to adjust or change oneor more parameters that may be associated with the pacing configurationcausing PS.

The decision module 228 can be configured to take action based on theoutcome of the PS test module 226, or to take action based on theoutcome of the recognition module 224, or to take action based on theoutcome of the trigger module 222. In an example, the decision module228 can be configured to store a PS presence indicator in the storage ofthe IMD 100, such as in the memory 210, based on the outcome of the PStest module 226. In an example, the decision module 228 can beconfigured to automatically switch the pacing configuration of the IMD100 to avoid PS. In an example, the decision module 228 can beconfigured to send an alert to an external system after the detection ofPS. In an example, the external system can be a programmer configured tocommunicate with the IMD 100. In an example, the external system cancommunicate with the IMD 100 over a telemetry link.

In an example, the user may desire automatic device adjustments to bemade to avoid PS. In an example, a physician can physically move theelectrode. Some examples can provide electronic repositioning byselecting a set of stimulation electrodes from a larger set of potentialstimulation electrodes. In some embodiments, the pacing vector betweenor among stimulation electrodes can be modified in an attempt to avoidPS. The controller 202 in some IMD 100 embodiments can include thepacing vector control module 218 which can be used to change the pacingvectors. The pacing vector control can be implemented under the controlof a clinician through an external programmer, or can be implementedautonomously by the IMD 100 such as in an ambulatory setting. The PSdetection can occur in the same IMD 100 that is providing the myocardialstimulation, or can occur in another internal system. In an example, theother internal system can be another IMD.

FIG. 3 illustrates an example of a system 300 that includes two or moreIMDs. A first one of the IMDs 100 in the illustrated system includes acardiac stimulator configured to deliver myocardial stimulation pulses.By way of example and not limitation, the first IMD 100 can be apacemaker or other cardiac rhythm management device. A second one of theIMDs 302 in the illustrated system includes a PS detector/sensor used todetect PS that can be caused by the myocardial stimulation pulsesdelivered from the first one of the IMDs. In an example, the PSdetector/sensor can include an accelerometer that can be configured todetect the presence of PS during myocardial stimulation. Theaccelerometer can provide a signal to the controller 202 of the IMD 100for use to detect PS. In some embodiments, the IMDs 100, 302 cancommunicate with each other over a wired connection. In someembodiments, the IMDs 100, 302 can communicate with each otherwirelessly using ultrasound or radiofrequency (RF) or other wirelesstechnology. The sensor(s) used for detecting PS can be implanted or canbe external. The algorithms for processing the sensed signals to detectPS can be performed within the IMD(s) and/or can be performed inexternal devices. In an example PS can be detected using the one or moresensors that can be implantable within the patient, while the processingof the sensed signals can be performed by external device(s). Themonitoring of the patient for PS can be performed in a clinical settingor in an ambulatory setting. This monitoring, regardless of whether itis performed in the clinical setting or an ambulatory setting, can beperformed using implanted PS detectors such as illustrated in FIGS. 2-3,for example, and/or can be performed using external PS detectors.

FIG. 4 illustrates an embodiment of a system that includes the IMD 100,such as a cardiac rhythm management device, an external device 402 suchas a programmer, and an external PS sensor 404. The system can beimplemented in a clinical setting, such as by a clinician who uses aprogrammer to program the IMD 100, or can be implemented by the patientin an ambulatory setting to occasionally check if the myocardialstimulation is causing PS. In an example, the external device 402includes a PS detector that cooperates with the PS sensor todiscriminate if a signal from the PS sensor indicates PS. In an example,the PS detector can be configured as the PS detector 220 discussed inFIG. 2. In various embodiments, the external device includes a PSthreshold test module used to perform PS threshold test(s). The PSthreshold test can be configured to control the IMD 100 to delivermyocardial stimulation using different stimulation parameters. The PSthreshold tests can be configured to determine the myocardialstimulation parameters that cause or that can cause PS, or myocardialstimulation parameters that do not cause PS. The physical position ofthe stimulation electrode or electrodes used to deliver the myocardialstimulation can be adjusted in an attempt to avoid PS, such as can occurduring an implantation procedure. In some examples, the pacing vectorbetween or among stimulation electrodes can be modified in an attempt toavoid PS. In some examples, the external PS sensor 404 can be integratedwith the external device 402, such that the PS can be sensed by holdingor otherwise positioning the external device next to the patient (e.g.externally positioned near the diaphragm or near the apex of the heart)to allow the PS sensor (e.g. an accelerometer in the device) to sensePS.

The external PS sensor 404 can include a two-axis or a three-axisaccelerometer for sensing PS in a pacing configuration of the IMD 100.As previously discussed, pacing pulses delivered by the IMD 100 canstimulate the phrenic nerve and cause contraction of the diaphragmresulting in PS presence. Abrupt contractions of the diaphragm can besensed by the accelerometer. The signal from the accelerometer can beused to detect PS which can be stored in the memory of the IMD alongwith the pacing configuration data. In some examples, PS detection andcorresponding PS data storing can be performed for all available pacingconfigurations or a subset of all available pacing configurations in theIMD 100.

FIG. 5 illustrates a system diagram of an example of a microprocessorbased implantable device. The controller of the device is amicroprocessor 502 which communicates with a memory 210 via abidirectional data bus. The controller can be implemented by other typesof logic circuitry (e.g., discrete components or programmable logicarrays) using a state machine type of design. As used herein, the term“circuitry” should be taken to refer to either discrete logic circuitry,firmware, or to the programming of a microprocessor. Shown in the figureare three examples of sensing and pacing channels. Each channel mayinclude a lead with a ring electrode 504 and a tip electrode, a sensingamplifier 508, a pulse generator 510, and a channel interface 512. Oneof the illustrated leads includes multiple ring electrodes 504, such ascan be used in a multi-polar lead. An example of a multipolar lead is aleft ventricle quadripolar lead. In some examples, the leads of thecardiac stimulation electrodes are replaced by wireless links. Eachchannel thus includes a pacing channel made up of the pulse generatorconnected to the electrode and a sensing channel made up of the senseamplifier connected to the electrode. The channel interfaces communicatebidirectionally with the microprocessor 502, and each interface caninclude analog-to-digital converters for digitizing sensing signalinputs from the sensing amplifiers and registers that can be written toby the microprocessor 502 in order to output pacing pulses, change thepacing pulse amplitude, and adjust the gain and threshold values for thesensing amplifiers 508. The sensing circuitry of the pacemaker detectsintrinsic chamber activity, termed either an atrial sense or ventricularsense, when an electrogram signal (i.e., a voltage sensed by anelectrode representing cardiac electrical activity) generated by aparticular channel exceeds a specified detection threshold. Pacingalgorithms used in particular pacing modes employ such senses to triggeror inhibit pacing. The intrinsic atrial and/or ventricular rates can bemeasured by measuring the time intervals between atrial and ventricularsenses, respectively, and used to detect atrial and ventriculartachyarrhythmias. The electrodes of each lead are connected viaconductors within the lead to a switching network 514 controlled by themicroprocessor. The switching network 514 is used to switch theelectrodes to the input of a sense amplifier in order to detectintrinsic cardiac activity and to the output of a pulse generator inorder to deliver a pacing pulse. The switching network 514 also enablesthe device to sense or pace either in a bipolar mode using both the ringand tip electrodes of a lead or in unipolar or an extended bipolar modeusing only one of the electrodes of the lead with the device housing(can) 516 or an electrode on another lead serving as the returnelectrode. In some examples, a shock pulse generator 518 can beinterfaced to the controller, in addition or alternative to otherstimulation channels, for delivering a defibrillation shock via a pairof shock electrodes 520 to the atria or ventricles upon detection of ashockable tachyarrhythmia. A can electrode can also be used to delivershocks. The figure illustrates a telemetry interface 522 connected tothe microprocessor 502, which can be used to communicate with anexternal device. As illustrated in FIG. 5, the system can include a PSsensor 206. According to various examples, the phrenic nerve activitydetector can include, but is not limited to, an accelerometer, anacoustic sensor, a respiration sensor, impedance sensors, neural sensoron the phrenic nerve, or electrodes to sense electromyogram signalsindicative of diaphragm contraction. Various examples use more than onedetector to provide a composite signal that indicates phrenic nervecapture. The use of more than one detector can enhance the confidence indetecting PS. The illustrated example also includes a clock 532.

According to various examples, the illustrated microprocessor 502 can beconfigured to perform various cardiac tissue (e.g. myocardial)stimulation routines 526. Examples of myocardial therapy routinesinclude bradycardia pacing therapies, antitachycardia shock therapiessuch as cardioversion or defibrillation therapies, antitachycardiapacing therapies (ATP), and cardiac resynchronization therapies (CRT).As illustrated, the controller 502 can also include a comparator 528 tocompare time when phrenic nerve activity is detected to a pace time todetermine that phrenic nerve activity is attributed to the pace, and/orcan includes a comparator 530 to compare respiration features to thepace time for use in detecting PS. The illustrated microprocessor 502can include instructions for performing a PS threshold test 216 and apacing vector control process 218, similar to the controller 502illustrated in FIG. 2. In an example, the PS threshold test 216 can beperformed to confirm the PS presence and can be performed by therecognition module 224 of the controller 502 as discussed in conjunctionwith FIG. 2.

The microprocessor 502 can control the overall operation of the IMD 100in accordance with programmed instructions stored in the memory 210. Inan example, the microprocessor 502 can be configured to perform thephrenic stimulation (PS) detection procedure. In an example where the PSsensor 206 includes an accelerometer, the PS detection procedure caninclude performing a base test by sensing the amplitude of theaccelerometer signal. The microprocessor 502 can further be configuredto compare the sensed amplitude of the signal to a threshold amplitudevalue. The PS data derived from the comparison can then be stored in thememory 210 of the IMD 100. For example, the microprocessor 502 canperform the base test for a current pacing configuration of the IMD 100implanted within a patient to detect the presence of PS and store theresults of the test. When the patient visits a physician during aregular check-up routine, the physician can check the data stored in thememory to check the suitability or performance of the IMD 100 in thecurrent pacing configuration. If the physician identifies that currentpacing configuration is causing PS, the physician can change theparameters of the current pacing configuration. The physician can alsoswitch the IMD 100 to another pacing configuration. In an example, thephysician can check the PS data for all the available pacingconfigurations in the IMD 100. The PS data may be acquired during avisit to the clinic, or when the patient is ambulatory away from theclinic. In an example, the PS data for all the pacing configurations canbe checked in accordance with the functioning of the PS test module 226of the ambulatory PS detector 220 as discussed previously in FIG. 2. ThePS data obtained from the PS test can be stored in the IMD 100 byperforming the PS procedure for all the available pacing configurationsin the IMD 100, and can be used as required.

FIGS. 6A-6E illustrate, by way of example, various embodiments of asystem 600 for performing a PS detection procedure, such as may beimplemented using a PS detector similar to PS detector 220 illustratedin FIG. 2. FIG. 6A illustrates a procedure in which a trigger moduletriggers a PS detection module. The PS detection module may include thedecision module 228 as illustrated in FIG. 6B, may include therecognition module 224 and decision module 228 as illustrated in FIG.6C, or may include the recognition module 224, PS test module 226 anddecision module 228 as illustrated in FIG. 6D. These modules have beenpreviously discussed with respect to FIG. 2. Some embodiments mayinclude the trigger module 222, the recognition module 224 and thedecision module 228. Some embodiments may include the trigger module222, the PS test module 226, and the decision module 228. A base test todetect PS may be performed, such as by trigger module 222, and anothertest may be performed to confirm the PS, such as by the recognitionmodule or the PS test module, and a decision can be made based on thetest results. In addition to performing the other test to confirm thePS, some embodiments may perform yet another PS detection test tofurther confirm the PS with greater confidence.

FIG. 6E illustrates an example in which the PS detection module includesthe recognition module 224, PS test module 226 and decision module 228,and also includes programmable instructions for controlling whichmodules are implemented in the PS detection module. For example, the toparrow from the trigger module 222 to the decision module 228 illustratesthat that recognition module 224 and PS test module 226 can be bypassed,and the bottom arrow from the recognition module 224 to the decisionmodule 228 indicates that the PS test module 226 can be bypassed.

FIG. 7 illustrates an example of using a threshold 604 for an amplitudeof signal from a PS sensor to trigger a PS detection routine. Forexample, the trigger module 222 illustrated in FIGS. 6A-6E may implementthe example. Amplitude values 606, 608 of the sensor signal (e.g.accelerometer signal) may be compared against the trigger threshold 604.Data collection is not continuous. The sensor signal may be sampled, andthe sampling of the sensor signal may be at a low sampling frequency. Ifthe amplitude value 606 is less than the trigger threshold 604, thetrigger module 222 does not trigger the PS detection routine but rathercontinues to monitor the PS sensor signal. If the amplitude value 608 isgreater than the trigger threshold 604, then the trigger module 222 maytrigger the PS detection routine.

The PS sensor signal may be collected continuously, such as by streamingthe signal. FIGS. 8A-8B illustrate an example of streaming signal froman accelerometer XL, where FIG. 8A illustrates no PS in the streamingsignal and FIG. 8B illustrates occurrences of PS in the streamingsignal. The recognition module 224 may evaluate a portion of thestreaming signal, in response to a trigger from the trigger module, todetect PS.

Analysis of the signal by the recognition module 224 can prevent falsepositive triggers from activating further PS presence search acrosspacing configurations, which can be a power intensive process. If theanalysis of the signal by the recognition module 224 confirms thepresence of PS, any of the full-test module 226 or the decision module228 can be activated.

In an example, the confirmation of the PS presence by the recognitionmodule 224 can activate the PS test module 226. The PS test module 226can be configured to analyze the signal from the accelerometer XL foreach of a plurality of potential pacing configurations from the two ormore pacing configurations that can be programmed in the IMD 100. Theplurality of potential pacing configurations can each have a differentcathode for delivering myocardial stimulation. More than one potentialpacing configuration may have a common cathode. The PS test module 226can be configured to analyze the signal from the accelerometer XL foreach cathode used in the potential pacing configurations. In an example,IMD 100 can be programmed for the plurality of pacing configurations. Inan example, the PS test module 226 can be configured to determine leftventricular thresholds for detecting PS in each of the plurality ofpotential pacing configurations. In an example, the PS test module 226can be configured to perform a test that can be programmed by a user ofthe IMD 100, such as either the physician or the patient, to analyze andconfirm PS for each of the plurality of potential pacing configurationsusing the PS test. In an example, the confirmation of PS presence by therecognition module 224 can activate the decision module 228. Thedecision module 228 can then be configured to take any of the actionsdiscussed previously to cause storing, reporting or mitigation of thePS.

FIGS. 9A-9B illustrate schematic diagrams for an example of performing aPS test across two potential pacing configurations and storing theresults of the test. Some examples include but are not limited toforcing a maximum output pacing limited by a ceiling in a current pacingvector or forcing a minimum output pacing limited by a floor in thecurrent vector. Some examples include a step-wise voltage/pulse widthtest. FIG. 9A illustrate a streaming PS sensor signal, and furtherindicate a signal in which PS is found (top) and a signal in which PS isnot found (bottom). Thus, the decision module 228 may record the PSresults (e.g. FIG. 9B) and may change the pacing configuration from LVTip→RV Vector to LV Ring→RV Vector to avoid PS.

As will be understood by those of ordinary skill in the art, at leastpart of the processes may be implemented using a machine or computerusing instructions encoded on a machine-readable or computer-readablemedium. It is to be understood that the above detailed description isintended to be illustrative, and not restrictive. Other embodiments willbe apparent to those of skill in the art upon reading and understandingthe above description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A system, comprising: an implantable medicaldevice (IMD) for implantation in a patient, the IMD including a cardiacpace generator, a phrenic nerve stimulation (PS) sensor, a memory, and acontroller, wherein the PS sensor is configured to provide a signal foruse in detecting PS, and the controller is operably connected to thecardiac pace generator to operate in a pacing configuration to generatecardiac paces, wherein the controller is configured to: perform a basetest when the cardiac pace generator is operating in the pacingconfiguration, including: monitor the signal provided from the PSsensor, including detect an amplitude of the monitored signal providedfrom the PS sensor, compare the sensed amplitude to a threshold todetect PS, and provide a trigger when the sensed amplitude is higherthan the threshold which indicates a PS detection from the monitoredsignal provided from the PS sensor: respond to the trigger from the basetest, wherein respond to the trigger includes: store a portion of thesignal from the PS sensor in the memory of the IMD when the cardiac pacegenerator is operating in the pacing configuration, wherein the storedportion is more than was used by the base test, the stored portionincluding N beats where a beat is a signal from the PS sensor associatedwith a cardiac pace: and analyze the stored portion of the signalincluding determining that M of N beats indicate PS to confirm the PSdetection from the base test, thereby providing a confirmed PS detectionhaving a higher level of confidence than provided by the base test thatPS is detected; and record, based on the confirmed PS detection, that PSis detected in the memory storage within the IMD.
 2. The system of claim1, wherein the controller is further configured to respond to theconfirmed PS detection, including further analyze the signal from the PSsensor using a different PS detection test to provide furtherconfirmation of the PS detection and thereby provide an even higherlevel of confidence that PS is detected than was provided by analyzingmore of the signal from the PS sensor.
 3. The system of claim 1, whereinthe controller is further configured to respond and to the confirmed PSdetection, including analyze the signal from the PS sensor for eachpotential pacing configuration in two or more potential pacingconfigurations to determine if PS is present in the two or morepotential pacing configurations.
 4. The system of claim 3, wherein eachof the two or more potential pacing configurations have a differentcathode, wherein the controller is configured to, in response to theconfirmed PS detection, analyze the signal from the PS sensor for eachcathode of the potential pacing configurations.
 5. The system of claim3, wherein the two or more potential pacing configurations are aprogrammed subset of IMD pacing configurations.
 6. The system of claim3, wherein the controller is configured to determine a PS threshold ineach of the two or more potential pacing configurations.
 7. The systemof claim 1, wherein the controller is configured to automatically changea current pacing configuration to another pacing configuration based atleast in part on PS detection.
 8. The system of claim 1, wherein thecontroller is configured to communicate an alert to an external devicebased at least in part on PS detection.
 9. The system of claim 1,wherein the PS sensor includes an accelerometer.
 10. A system,comprising: an implantable medical device (IMD) for implantation in apatient, the IMD including a cardiac pace generator, a memory, acontroller and a phrenic nerve stimulation (PS) sensor including anaccelerometer, wherein the PS sensor is configured to provide a signalfor use in detecting PS, and the controller is operably connected to thecardiac pace generator to operate in a pacing configuration to generatecardiac paces, wherein the controller is configured to: perform a basetest when the cardiac pace generator is operating in the pacingconfiguration, including: monitor the signal provided from the PSsensor, including detect an amplitude of the monitored signal providedfrom the PS sensor, compare the sensed amplitude to a threshold todetect PS, and provide a trigger when the sensed amplitude is higherthan the threshold which indicates a PS detection from the monitoredsignal provided from the PS sensor; respond to the trigger from the basetest, wherein respond to the trigger includes: store a portion of thesignal from the PS sensor in the memory of the IMD when the cardiac pacegenerator is operating in the pacing configuration, wherein the storedportion that is more than was used by the base test , the stored portionincluding N beats where a beat is a signal from the PS sensor associatedwith a cardiac pace; and analyze the stored portion of the signalincluding determining that M of N beats indicate PS, thereby providing aconfirmed PS detection, having a higher level of confidence thanprovided by the base test that PS is detected; respond to the confirmedPS detection, including further analyze the signal from the PS sensorusing a different PS detection test to provide greater confidence thatPS is detected; and record, based on the confirmed PS detection, PSdetection in the memory storage within the IMD and: automatically changea current pacing configuration to another pacing configuration based atleast in part on the confirmed PS detection; or communicate an alert toan external device based at least in part on the confirmed PS detection.11. The system of claim 10, wherein the controller is configured torespond to a user input to selectively skip the further analysis of thesignal from the PS sensor or to selectively skip both the analysis andthe further analysis of the signal from the PS sensor.
 12. A system,comprising: an implantable medical device (IMD) for implantation in apatient, the IMD including a cardiac pace generator, phrenic nervestimulation (PS) sensor, a memory, and a controller, wherein the PSsensor is configured to provide a signal for use in detecting PS, andthe controller is operably connected to the cardiac pace generator tooperate in a pacing configuration to generate cardiac paces, wherein thecontroller is configured to: perform a base test when the cardiac pacegenerator is operating in the pacing configuration, including: monitorthe signal provided from the PS sensor, including detect an amplitude ofthe monitored signal provided from the PS sensor, compare the sensedamplitude to a threshold to detect PS, and provide a trigger when thesensed amplitude is higher than the threshold which indicates a PSdetection from the monitored signal provided from the PS sensor; respondto the trigger from the base test, wherein respond to the triggerincludes: store a portion of the signal from the PS sensor in the memoryof the IMD when the cardiac pacing generator is operating in the pacingconfiguration, wherein the stored portion is more than was used by thebase test, the stored portion including N beats where a beat is a signalfrom the PS sensor associated with a cardiac pace; and analyze thestored portion of the signal including determining that M of N beats areconsistent with PS to confirm the PS detection from the base test,thereby providing a confirmed PS detection having a higher level ofconfidence than provided by the base test that PS is detected; andrecord, based on the confirmed PS detection, that PS is detected in thememory storage within the IMD and automatically change a current pacingconfiguration to another pacing configuration based at least in part onthe confirmed PS detection.
 13. The system of claim 12, wherein thecontroller is further configured to respond to the confirmed PSdetection, including further analyze the signal from the PS sensor toprovide further confirmation of the PS detection and thereby provide aneven higher level of confidence that PS is detected than was provided byanalyzing more of the signal from the PS sensor.
 14. The system of claim13, wherein the controller is configured to determine a PS threshold ineach of the two or more potential pacing configurations.
 15. The systemof claim 12, wherein the controller is further configured to respond tothe confirmed PS detection, including analyze the signal from the PSsensor for each potential pacing configuration in two or more potentialpacing configurations to determine if PS is present in the two or morepotential pacing configurations.
 16. The system of claim 15, whereineach of the two or more potential pacing configurations have a differentcathode, wherein the controller is configured to respond to theconfirmed PS detection, including analyze the signal from the PS sensorfor each cathode of the potential pacing configurations.
 17. The systemof claim 15, wherein the two or more potential pacing configurations area programmed subset of IMD pacing configurations.
 18. The system ofclaim 12, wherein the controller is configured to communicate an alertto an external device based at least in part on PS detection.